1. Field of the Invention
The present invention relates to a communication apparatus used in mobile communication and, more particularly, to an oscillating apparatus which prevents a degradation in phase noise characteristics due to vibrations.
2. Description of the Prior Art
Various physical countermeasures are applied to a conventional oscillator used as the local oscillating circuit of a communication apparatus to prevent a degradation in phase noise characteristics due to vibrations. For example, an oscillator used when a station is stationary employs a structure in which a vibration element is fixed with an adhesive having a small elastic coefficient. An oscillator used in a mobile station adopts a structure in which a vibration element is supported by springs.
FIG. 1 is a view showing the former case which is disclosed in Japanese Unexamined Utility Model Publication No. 2-108429. A crystal resonator 61 is sealed in a holder 62 and mounted on a print board 64 having thin annealed copper wires 66 connected to electrode lead wires 63 of the holder 62. The holder 62 is fixed to the print board 64 with an adhesive 65 having a small elastic coefficient. With this structure, mechanical vibrations added to the print board 64 are hardly transmitted to the crystal resonator 61.
FIG. 2 is a view showing the latter case. A crystal resonator 71 is supported by eight springs 72 in a holder 73. Mechanical vibrations added to the holder 73 are absorbed by the springs 72, thereby preventing transmission of the vibrations to the crystal resonator 71.
Of the above-described conventional countermeasures against vibrations, the former is limited in reduction of the elastic coefficient of the adhesive. For this reason, it is difficult to effectively prevent transmission of vibrations from the print board 64 to the quartz crystal oscillator 61, and a large improvement effect can hardly be expected. The latter can obtain a larger improvement effect by appropriately setting the spring constant of the springs 72. However, when the entire structure becomes bulky, the improvement amount receives influences of the mounting method and varies. Depending on the set value of the spring constant, the effect varies in accordance with a vibration frequency. Especially, when the springs are resonant with vibrations, a greater degradation may be undesirably caused.